Transplacental passage of WEHI-3 tumor viruses induce lymphomas in offspring suggesting that immunologic responses to them have not been elicited; adult BALB/c mice cannot reject these tumor-inducing viruses; these viruses are in some instances sequestered and/or produced with the bone matrix; demyelinization of spinal cord axons and the presence of virus in the spinal cord may be related phenomena in animals that develop the hind leg paralysis. Preliminary results of administration of adriamycin to normal newborn chicks suggest non-specific toxicity with occasional pericardial, myocardial and hepatic lesions. In the invertebrate model, normal development of the larva is seriously impaired and lesions in the thoracic dorsal vessel (analogue to the vertebrate heart) are similar to those reported in adriamycin induced cardiac toxicity in humans. The value of using these models remains to be evaluated.